Now that the internet exists, it's harder to reason about how hard a breakthrough was to make. Before information was everywhere instantly, it would be common for discoveries to be made concurrently, separated by years, but genuinely without either scientist knowing of the others work.

That distance between when the two (or more) similar discoveries happened gives insight into how difficult it was. Separated by years, and it must have been very difficult. Separated by months or days, and it is likely an obvious conclusion from a previous discovery. Just a race to publish at that point.